For the formation of color photographic images, three photographic color couplers of yellow, magenta and cyan are incorporated into photographic layers of a photographic material, and the material is exposed to light and then developed with a color developer containing a color developing agent. In said process, an oxidation product of an aromatic primary amine is reacted with a coupler by a coupling reaction, whereby a color-forming dye is formed. In the formation of said color-forming dye, it is preferred that the coupling reaction speed is as high as possible and that the coupler has a higher color formability, so that a color image having a higher color density may be obtained within a limited shorter developing period of time. In addition, it is required that the color-forming dyes are sharp yellow, magenta and cyan dyes each with less side absorption and that color photographic images of good color reproduction are obtained.
Under the circumstances, the role of the couplers is great, and therefore, various studies have heretofore been made for the modification of the structures of various couplers to improve them. In particular, magenta couplers are important in view of the luminosity thereof, and 5-pyrazolone derivatives have essentially been used therefor.
However, color images as formed from the magenta couplers of said 5-pyrazolone derivatives not only have an absorption in the green light region but also have some unnecessary absorption in the blue light region and red light region, and therefore, it cannot be said as yet that said magenta couplers have sufficient coloring characteristics. In addition 5-pyrazolone derivatives are apt to decompose and yellow when exposed to light or kept under high humidity, and therefore, these are unsatisfactory in view of the preservation stability of the formed images.
On the other hand, it is indispensable to severely control the gradation in the color photographic images in order to improve the color reproduction and the tone reproduction of said images. When the gradation control is insufficient, the color reproduction of the formed image is bad even if the best couplers are used, and further, the tone reproduction in the highlight or shadow in the formed color photographic images is extremely deteriorated.
For control of the gradation, for example, Japanese Patent Application (OPI) No. 150841/82 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") has proposed a method for attaining soft gradation where a sensitizing dye is added to each of two or more monodispersed emulsions each having a different grain size in such a manner that the amount of said sensitizing dye to be added to an emulsion having a larger grain size is to be larger, per unit surface area of the particles and said emulsions are blended.
Following said proposal, the present inventors tried to blend plural monodispersed emulsions each having a different sensitivity and containing said magenta coupler of a 5-pyrazolone derivative for the purpose of attaining the desired gradation. However, the color reproduction was not improved in this trial.